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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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because of increase in glacial erosion by the united Barry Ann and College Fiord Glaciers. These submerged steps are apparently the same as the rock treads produced by differential glacial erosion on the land. The lip of the submerged tread of the Barry Arm step is 354 feet higher than the bottom of Port Wells; but if the ridge interpreted as a submerged moraine is added the discordance is 576 feet in all.
The next three soundings in Port Wells, a mile apart, show depths of 1098 to 1200 feet (Fig. 49); and the following seven soundings, two miles apart, show depths of 1296 to 1404 feet. The bottom slope of Port Wells, therefore, averages 28 feet to the mile, being a little flatter than the bottom slope of Barry Arm (PI. CXL) above the step.
Cross-Sections of Fiords. The cross-sections of southern Port Wells and outer Passage Canal show a fiord bottom 1400 feet deep and between two and three miles wide, bordered by sides sloping 1000 to 1200 feet to the mile. Such a cross-section is characteristic of a glacially-eroded fiord, and is repeated in narrower sections throughout Port Wells, Barry Arm, and Harriman Fiord.
Submerged Hanging Valleys. Pigot Bay is a submerged hanging valley (Fig. 49), with water 330 to 408 feet deep, and with the lip 1038 feet above the fiord bottom. Bettels Bay and the small indentations on the western side of Port Wells may be presumed to have a similar discordant relationship though no soundings were made. The indentation south of Bettels Bay is barred at the mouth by rock islands, and if the channels between are shallow, as is probable, the discordance of grade here is over 1300 feet. Submerged hanging valleys are also suspected in the coves on the eastern side of Port Wells south of Esther Passage. This passage itself has a hanging relationship to Port Wells, the water being 66 feet deep at its entrance, while the main Port Wells fiord is 1200 feet deep.
A large valley on the eastern side of Barry Arm joins the fiord at sea level, and if there are rock ledges near the mouth it hangs over 600 feet above the fiord bottom.
The deposits near the mouth of Surprise Glacier inlet make it impossible to determine the erosion relationship of Surprise and Harriman Glaciers; but, though this cannot be stated positively, it seems probable from the existing depths that the inlet of Surprise Glacier hangs 100 feet or more above that of Harriman Glacier. However, the cove in which Serpentine Glacier terminates, is clearly a submerged hanging valley, the depth of water being 12 to 51 feet near the glacier front, and 474 feet in the fiord opposite, so that the total amount of discordance is at least 423 feet (Fig. 50).
Partly as a result of the steepness of the fiord walls, the glacial deposits in these fiords are not extensive. They include a veneer of ground moraine on all but the steeper slopes, small belts of lateral moraine on the fiord walls, some areas of outwash plain, and some terminal moraines above and below .sea level.
Moraine. The areas of ground moraine call for no particular description. They consist of till and bowlders of various sorts, including rock carried out from the mountains and not present in the country rock of the region near where they lie. There are doubtless deposits of similar material and of fine silts below sea level in the fiords, but of the nature and distribution of these nothing is known.
The lateral moraines are especially well developed near some of the existing glaciers,